Stlhead is describing the bed, bread & head rule. (sleeping arrangements, permanent cooking facilities, and a bathroom) Works for boats, RV's, etc. Essentially counts as a second home. Interest is deductible (check with your accountant)

Consumers also get tax breaks for upgrading to energy efficient windows, and buying one of those nifty hybrids cars. While not depreciation, it is an incentive to invest.

The Government uses incentives to achieve goals, such as having healthy industry, which provides jobs, and hopefully creates a happy populace. (In a perfect world)

Just as economics is based on a perfect world, so is politics. Glad to know we both have some education on theoretical economics and experience with the real world as well. Unfortunately, I live here, not there.